1. Field of the Invention
The present invention relates to a paper material refining apparatus used in, for example, paper making and pulp industries. More particularly, the present invention is concerned with a paper material refining apparatus having a drum-type screen plate and a drum-type rotor.
2. Description of the Related Art
FIG. 3 shows a known paper material refining apparatus of a type in which a paper material is refined by being passed through a flat screen plate. This type of paper material refining apparatus is disclosed, for example, in Japanese Patent Laid-Open Publication No. 1-250487 and the specification of U.S. Pat. No. 4,913,359.
In the conventional paper material refining device, the paper material is supplied through a material supply pipe 5. The material supplied through the material supply pipe 5 often contains foreign matters such as metal pieces. It is often experienced that the foreign matters such as metal pieces are jammed between a flat screen plate 2' and an impeller 8' of the refining apparatus, with the result that the flat screen plate 2' and the impeller 8' are broken.